EP0422702A2 - Magneto-elastischer Drehmomentwandler - Google Patents

Magneto-elastischer Drehmomentwandler Download PDF

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Publication number
EP0422702A2
EP0422702A2 EP90125788A EP90125788A EP0422702A2 EP 0422702 A2 EP0422702 A2 EP 0422702A2 EP 90125788 A EP90125788 A EP 90125788A EP 90125788 A EP90125788 A EP 90125788A EP 0422702 A2 EP0422702 A2 EP 0422702A2
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EP
European Patent Office
Prior art keywords
torque
shaft
bands
region
transducer
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Granted
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EP90125788A
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English (en)
French (fr)
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EP0422702A3 (en
EP0422702B1 (de
Inventor
Ivan J. Garshelis
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Mag Dev Inc
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Mag Dev Inc
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Priority claimed from US06/938,404 external-priority patent/US4760745A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
    • G01L3/02—Rotary-transmission dynamometers
    • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
    • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
    • G01L3/02—Rotary-transmission dynamometers
    • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
    • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
    • G01L3/101—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means
    • G01L3/102—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means involving magnetostrictive means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
    • G01L3/02—Rotary-transmission dynamometers
    • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
    • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
    • G01L3/101—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means
    • G01L3/102—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means involving magnetostrictive means
    • G01L3/103—Details about the magnetic material used
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
    • G01L3/02—Rotary-transmission dynamometers
    • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
    • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
    • G01L3/101—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means
    • G01L3/105—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving magnetic or electromagnetic means involving inductive means

Definitions

  • the present invention relates to torque sensors and, more particularly, to non-contacting magnetoelastic torque transducers for providing a measure of the torque applied to a rotary shaft.
  • All magnetoelastic torque transducers have two features in common -- (1) a torqued member which is ferromagnetic and magnetostrictive, the former to ensure the existence of magnetic domains and the latter to allow the orientation of the magnetization within each domain to be altered by the stress associated with applied torque; and (2) a means, most usually but not necessarily electromagnetic means, for sensing variations from the untorqued distribution of domain orientations.
  • a torqued member which is ferromagnetic and magnetostrictive, the former to ensure the existence of magnetic domains and the latter to allow the orientation of the magnetization within each domain to be altered by the stress associated with applied torque
  • a means, most usually but not necessarily electromagnetic means for sensing variations from the untorqued distribution of domain orientations.
  • each element in the shaft is subjected to a shearing stress.
  • This shearing stress may be expressed in terms of a tensile stress and an equal and perpendicular compressive stress, with the magnitude of each stress being directly proportional to the distance between the shaft axis and the element.
  • the directions of maximum tension and compression occur along tangents to 45° left-handed and 45° right-handed helices about the axis of the shaft.
  • the effect of the torque is to increase the magnetic permeability in directions parallel to one of the helices and, correspondingly, to decrease the magnetic permeability in directions parallel to the other of the helices.
  • Magnetic Measurements of Torque in a Rotating Shaft The Review of Scientific Instruments, Vol. 25, No. 6, June, 1954, Beth and Meeks suggest that in order to use permeability change as a measure of the applied torque, one should monitor permeability along the principal stress directions and pass the magnetic flux through the shaft near its surface. This is because the stress is greater, the further the element is from the shaft axis and it is along the principal stress directions that the maximum permeability change is expected.
  • Patent No. 3,340,729 - Scoppe is to rigidly affix, as by welding, a magnetic sleeve to the load-carrying shaft so that a torsional strain proportional to the torsional load is imparted to the sleeve.
  • the measuring device employed now senses permeability changes in the rotating sleeve rather than in the rotating shaft. This permits, according to Scoppe, a material to be selected for the shaft which optimizes the mechanical and strength properties required for the shaft while a different material may be selected for the sleeve which optimizes its magnetic properties.
  • the Scoppe torquemeter utilized a primary winding for generating a magnetic flux and two secondary windings, one oriented in the tension direction and the other in the compression direction.
  • annealing the shaft and sleeve to remove these stresses also anneals away desirable mechanical properties in the shaft and changes the magnetic properties of the sleeve.
  • the shortcomings of Scoppe's transducer due to its need to monitor permeability changes lying along the principal stress directions, are its sensitivity to variations in its radial distance from the shaft, magnetic inhomogeneity around the shaft circumference and dependence on shaft speed.
  • a different approach to magnetoelastic torque sensing utilizes the differential magnetic response of two sets of amorphous magnetoelastic elements adhesively attached to the torqued shaft.
  • This approach has the advantage over prior approaches that it is insensitive to rotational position and shaft speed. However, it requires inordinate care in the preparation and attachment of the elements.
  • transducer performance is adversely affected by the methods used to conform the ribbon elements to the shape of the torqued member; the properties of the adhesive, e.g., shrinkage during cure, expansion coefficient, creep with time and temperature under sustained load; and, the functional properties of the amorphous material itself, e.g., consistency, stability.
  • Still another concern is in the compatibility of the adhesive with the environment in which the transducer is to function, e.g., the effect of oil, water, or other solvents or lubricants on the properties of the adhesive.
  • Harada et al. disclose a torque transducer formed by gluing two circumferential stress-sensitive amorphous ribbons to a shaft at axially spaced apart locations. Unidirectional magnetoelastic magnetic anisotropy is created in each ribbon by torquing the shaft in a first direction, gluing a first ribbon to it, releasing the torque to set-up elastic torque stresses within the first ribbon, torquing the shaft in the opposite direction, gluing the second ribbon to it, and then releasing the torque to set-up elastic torque stresses within the second ribbon.
  • the anisotropy in one ribbon lies along a right-hand helix at +45° to the shaft axis while the anisotropy in the other ribbon lies along an axially symmetric left-hand helix at -45° to the shaft axis.
  • AC powered excitation coils and sensing coils surround the shaft making the transducer circularly symmetric and inherently free from fluctuation in output signal due to rotation of the shaft.
  • the magnetization within the two ribbons will respond symmetrically to equal axial magnetizing forces and the sensing coils will detect no difference in the response of the ribbons.
  • Amorphous ribbons have also been glued to a shaft in a ⁇ 45° chevron pattern, see Sasada et al., IEEE Trans. on Mag., MAG-20, No. 5, 951-53, 1984, and amorphous ribbons containing parallel slits aligned with the ⁇ 45° directions have been glued to a shaft, see, Mohri, IEEE Trans. on Mag., MAG-20, No. 5, 942-47, 1984, to create shape magnetic anisotropy in the ribbons rather than magnetic anisotropy due to residual stresses.
  • Other recent developments relevant to the use of adhesively attached amorphous ribbons in a magnetoelastic torque transducer are disclosed in U.S. Patent No. 4,414,855 - Iwasaki and U.S. Patent No. 4,598,595 - Vranish et al.
  • USSR Certificate No. 274,420 discloses a magnetoelastic torque measuring device, not unlike the Harada et al amorphous ribbon transducer, comprising a pair of sleeves which are initially deformed by applied torques of different directions to endow the sleeves with oppositely directed magnetic anisotropy and then mounted on a shaft in annular grooves formed therein.
  • the grooves have a radial depth selected to accomodate the sleeves therewithin with the outer diameter of the sleeves coplanar with the outer surface of the shaft.
  • 667,836 discloses a magnetoelastic torque transducer having two axially spaced-apart circumferential bands on a shaft, the bands being defined by a plurality of slots formed in the shaft in a ⁇ 45° chevron pattern, and a pair of excitation and measuring coil-mounting circumferential bobbins axially located along the shaft so that a band underlies each bobbin.
  • the shape anisotropy created by the slots is the same type of magnetic preconditioning of the shaft as was created, for example, by the chevron-patterned amorphous ribbons of Sasada et al and the slitted amorphous ribbons of Mohri, and suffers from many of the same shortcomings.
  • 169,326 discloses means for measuring the torque in a rotating shaft formed of ferromagnetic material.
  • the means includes a pair of axially spaced-apart bands on the shaft surface, the bands having knurls formed thereon at opposite angles of ⁇ 45° and coils surrounding the respective bands for sensing the change in magnetic flux when torque is applied to the shaft and for generating an emf proportional to the applied torque.
  • the bands include at least one circumferential region which is free of residually unstressed areas over at least 50% of its circumferential length.
  • the reference to the knurl "hills" in one band being subjected to a compressive stress while the knurl "hills" in the other band are subjected to a tensile stress suggest that the magnetic anisotropy results from the macroscopic topographic alteration of the shaft surface, i.e., the knurl, rather than from any residual stress created by a mechanical working process leading to the knurl.
  • 838,448 also discloses a magnetoelastic torque transducer having two spaced-apart circumferential bands on a shaft, circumferential excitation coils and circumferential measuring coils surrounding and overlying the bands.
  • the bands are formed by creating a knurl in the shaft surface with the troughs of the knurl at ⁇ 45° angles to the shaft axis so that the troughs in one band are orthogonal to the troughs in the other band.
  • the knurls are carefully formed by an undisclosed method which ensures the presence of substantial unstressed surface sections between adjacent troughs so that the magnetic permeability of the troughs is different from the magnetic permeability of the unstressed areas therebetween.
  • the trough width-to-pitch ratio corresponds to the stressed to unstressed area ratio and the desired ratio appears to be 0.3
  • This very minimal stress anisotropic preconditioning is believed to be too small to provide a consistent transducer sensitivity, as measured by the electronic signal output of the measuring coils and their associated circuitry, for economical commercial utilization.
  • a magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member in which a ferromagnetic and magnetostrictive region of the torqued member serves as a part of the magnetic sensing circuit of the transducer by providing at the surface of said region a pair of axially spaced-apart annular bands endowed with residual stress created, respectively symmetrical, left and right hand helically directed magnetic anisotropy of relatively large magnitude, which anisotropy overwhelms and/or renders negligible or insignificant any random anisotropy in the member as a result of internal stresses due to mechanical working, inhomogeneities, crystal orientation, and the like.
  • a magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member in which a thermally hardened ferromagnetic, magnetostrictive region of the torqued member or a thermally hardened ferromagnetic, magnetostrictive means rigidly affixed to or associated with the surface of said torqued member serves as a part of the magnetic sensing circuit of the transducer by providing at the surface of said thermally hardened region or means a pair of axially spaced-apart annular bands endowed with residual stress created, respectively symmetrical, left and right hand helically directed magnetic anisotropy of relatively large magnitude, which anisotropy overwhelms and/or renders negligible or insignificant any random anisotropy in the member as a result of internal stresses due to mechanical working, inhomogeneties, crystal orientation, and the like.
  • thermally hardened means heat treated at elevated temperatures above about 800°C., e.g., by annealing followed by quenching or by case hardening at high temperatures in a carburizing atmosphere followed by quenching, to impart desirable mechanical properties, e.g., hardness and strength, to the material of which the member, region or means is formed.
  • a magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member, said member having a ferromagnetic and magnetostrictive region, said transducer comprising a pair of axially spaced-apart annular bands defined within said region, said bands having, at least at the surface of said member, respectively symmetrical right and left hand helically directed residual stress created magnetic anisotropy, each said band having at least one circumferential region which is free of residually unstressed areas, i.e., said at least one circumferential region is residually stressed, over at least 50% of its circumferential length; means for applying a cyclically time varying, e.g., alternating, magnetic field to said bands; means for sensing the change in permeability of said bands caused by said applied torque; and means for converting said sensed change in permeability to an electrical signal indicative of the magnitude of the torque applied to said member.
  • the ferromagnetic and magnetostrictive region is formed of an iron-nickel martensite hardenable steel, such as a nickel maraging steel, or a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of one or more elements selected from Ni, Cr, Co, Ti, Al, Mn, Mo, Cu and B to raise the alloy magnetostriction to at least 5 ppm absolute.
  • an iron-nickel martensite hardenable steel such as a nickel maraging steel, or a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of one or more elements selected from Ni, Cr, Co, Ti, Al, Mn, Mo, Cu and B to raise the alloy magnetostriction to at least 5 ppm absolute.
  • the present invention contemplates a magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member, including ferromagnetic, magnetostrictive means rigidly affixed to, associated with or forming a part of the surface of said torqued member for altering in magnetic permeability in response to the application of torque to said member, means for applying a magnetic field to said ferromagnetic, magnetostrictive means, means for sensing the change in permeability caused by said applied torque and means for converting said sensed change in permeability to an electrical signal indicative of the magnitude of the torque applied to said member, the ferromagnetic, magnetostrictive means being formed of an iron-nickel martensite hardenable steel, such as a nickel maraging steel, or a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of one or more elements selected from Ni, Cr,
  • a method of sensing the torque applied to a member having a ferromagnetic and magnetostrictive region which includes the steps of endowing a pair of axially spaced-apart annular bands within said region with respectively symmetrical, right and left hand helically directed magnetic anisotropy, applying a cyclically time varying, e.g., alternating, magnetic field to said bands and sensing the permeability difference between said bands resulting from the application of torque to said member, the difference being indicative of the magnitude of the applied torque, the improvement which comprises forming said bands at the surface of said member and endowing said bands with magnetic anisotropy by instilling a residual stress distribution in each band which is sufficiently extensive that at least one circumferential region within each band is free of residually unstressed areas, i.e., said at least one circumferential region is residually stressed, over at least 50% of its circumferential length.
  • the ferromagnetic and magnetostrictive region is formed of an iron-nickel martensite hardenable steel, such as a nickel maraging steel, or a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of one or more elements selected from Ni, Cr, Co., Ti, Al, Mn, Mo, Cu and B to raise the alloy magnetostriction to at least 5 ppm absolute.
  • an iron-nickel martensite hardenable steel such as a nickel maraging steel, or a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of one or more elements selected from Ni, Cr, Co., Ti, Al, Mn, Mo, Cu and B to raise the alloy magnetostriction to at least 5 ppm absolute.
  • a method of sensing the torque applied to a member having a ferromagnetic and magnetostrictive region which includes the steps of endowing said region with helically directed magnetic anisotropy by instilling a residual stress distribution in said region which is sufficiently extensive that at least one circumferential region within said ferromagnetic and magnetostrictive region is free of residually unstressed areas, i.e., said at least one circumferential region is residually stressed, over at least 50% of its circumferential length, applying a cyclically time varying, e.g., alternating, magnetic field to said ferromagnetic and magnetostrictive region and to an area of said member not so endowed, and sensing the permeability difference between said ferromagnetic and magnetostrictive region and said area resulting from the application of torque to said member, the difference being indicative of the magnitude of the applied torque.
  • the ferromagnetic and magnetostrictive region is formed of an iron-nickel martensite hardenable steel, such as a nickel maraging steel, or a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of one or more elements selected from Ni, Cr, Co, Ti, Al, Mn, Mo, Cu and B to raise the alloy magnetostriction to at least 5 ppm absolute.
  • an iron-nickel martensite hardenable steel such as a nickel maraging steel, or a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of one or more elements selected from Ni, Cr, Co, Ti, Al, Mn, Mo, Cu and B to raise the alloy magnetostriction to at least 5 ppm absolute.
  • a method for making a magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member comprising the steps of providing a member having a ferromagnetic and magnetostrictive region; thermally hardening said region; endowing said thermally hardened region with a pair of axially spaced-apart annular bands having respectively symmetrical, right and left hand helically directed residual stress created magnetic anisotropy, each said band having at least one circumferential region which is free of residually unstressed areas over at least 50% of its circumferential length; providing excitation means associated with said bands for applying a cyclically time varying, e.g., alternating, magnetic field to said bands; providing sensing means associated with said bands for sensing the change in permeability of said bands caused by said applied torque; and, providing means for converting said sensed change in permeability to an electrical signal indicative of the magnitude of the torque applied to said member.
  • Figure 1 is a perspective view of a magnetoelastic torque transducer in accordance with the present invention
  • Figure 2 is a sectional view of a magnetoelastic torque transducer in accordance with the present invention illustrating one form of magnetic discriminator useful therewith
  • Figure 3 is a circuit diagram showing the circuitry associated with the magnetic discriminator of Figure 2
  • Figure 4 is a schematic view of a magnetoelastic torque transducer in accordance with the present invention illustrating another form of magnetic discriminator, and its associated circuitry, useful therewith
  • Figure 5 is a graphical representation of the relationship between applied torque and output signal for several magnetoelastic torque transducers of the present invention
  • Figure 6 is a graphical representation of the relationship between applied torque and output signal for the magnetoelastic torque transducers of Figure 5 after the shafts thereof have been heat treated under identical conditions
  • Figure 7 is a graphical representation of the general relationship between torque transducer sensitivity and residual stress loading along the
  • Figures 10, 11 and 12 are graphical representations of the relationship between applied torque and output signal for magnetoelastic torque transducers made in accordance with the present invention.
  • a magnetoelastic torque transducer comprising (1) a torque carrying member at least the surface of which, in at least one complete circumferential region of suitable axial extent, is appropriately ferromagnetic and magnetostrictive; (2) two axially distinct circumferential bands within this region or one such band in each of two such regions that are endowed with respectively symmetrical, helically directed residual stress induced magnetic anisotropy such that, in the absence of torque, the magnetization tends to be oriented along a left-hand (LH) helix in one band and along an axially symmetrical right-hand (RH) helix in the other band; and (3) a magnetic discriminator device for detecting, without contacting the torqued member, differences in the response of the two bands to equal, axial magnetizing forces.
  • LH left-hand
  • RH right-hand
  • FIG. 1 a cylindrical shaft 2 formed of ferromagnetic and magnetostrictive material or, at least having a ferromagnetic and magnetostrictive region 4, is illustrated having a pair of axially spaced-apart circumferential or annular bands 6,8 endowed with respectively symmetrical, helically directed magnetic stress anisotropy in the angular directions ⁇ ⁇ of the respective magnetic easy axes 10,12.
  • a magnetic discriminator 14 is spaced from shaft 2 by a small radial space. In the absence of applied torque the magnetization within the bands 6,8 will respond symmetrically to the application of equal axial magnetizing forces.
  • the torque carrying member is provided with two axially spaced-apart, distinct circumferential or annular bands in the ferromagnetic region of the member.
  • the bands are intentionally endowed with respective symmetrical, helically directed, magnetic anisotropy caused by residual stress. Residual stress may be induced in a member in many different ways, as discussed more fully hereinbelow.
  • the angular direction of the tangential principal residual stress with the member's axis will vary between values greater than zero and less than 90°.
  • the angular direction of the residual stress and that of the resulting magnetic easy axes is from 10°-80° and, most desirably, from 20° 60°.
  • residual stresses are those stresses that exist in a body in the absence of external forces. Their distribution is such that the net forces and moments acting on various regions within the body sum to zero on the whole body. Thus, if any one region exerts net forces and/or torques on the remainder of the body then other regions must exert compensating forces and/or torques. The consequence of this requirement for residual stresses to establish self-compensating distributions is that the existence of any region experiencing a tensile stress implies the existence of a communicating region experiencing compressive stress. Residual stress is often classified by the size of the regions and the distances separating compensating regions as short range (SR) and long range (LR). SR stresses exist in regions from a few atoms up to a size comparable to microstructural features such as a single grain. LR stresses exist over dimensions from more than one grain to macroscopic features of the whole body.
  • SR short range
  • LR stresses long range
  • the sensing of torque is primarily accomplished by sensing the change in permeability at the surface of the torqued member, it is at least at the surface of each band that there must be magnetic anisotropy created by residual stress.
  • the limitation that the applied stress must be at least sufficient to exceed the elastic limit of the member at its surface.
  • the application of an applied stress exceeding the minimum will, depending upon the magnitude of the applied stress, result in residual stress within the body of the member as well.
  • the term "surface" of the member means at the surface and within 0.010 inch thereof.
  • any method of applying stress to a member to exceed the elastic limit thereof at the surface of the bands may be employed which produces uneven plastic deformation over the relevant cross-section of the member.
  • the residual stress inducing method may be mechanical, thermal, or any other which is suitable. It is particularly desirable that the residual stress-inducing applied stress exceed the maximum expected applied stress when the member is torqued in use. This is to insure that torquing during use does not alter the residual stress pattern and, thus, the magnetic anisotropy within the bands.
  • the residual stress induced in the respective bands should be substantially equal and symmetrical in order that axial permeability sensing, when equal axial magnetizing forces are applied to the member, will produce a "no difference" output in the untorqued condition and equal but opposite output as a result of the application of equal clockwise (CW) and counter-clockwise (CCW) torques.
  • the method chosen to apply stress to a member beyond the elastic limit thereof in order to create residual stress is largely a function of the member's size, shape, material and intended application.
  • the method may induce continuous and substantially equal residual stresses over the entire surface of the band, i.e., around the entire band circumference and along its entire axial length.
  • the method may induce a residual stress pattern within each band which includes both stressed and unstressed areas.
  • Such a pattern is subject to the important limitation that each band must have at least one continuous circumferential region which is free of unstressed areas over at least 50% of its circumferential length, desirably over at least 80% of its circumferential length.
  • each band would have at least one continuous circumferential region which is free of unstressed areas over its entire circumferential length.
  • the term "circumferential region” means the locus of points defining the intersection of (1) a plane passing perpendicular to the member's axis and (2) the surface of the member, as hereinbefore defined.
  • the circumferential region is a circle defining the intersection of the cylindrical surface with a plane perpendicular to the shaft axis, and such a circle has a circumference or circumferential length. Stated otherwise, if each element of the member's surface comprising the circumferential region were examined, it would be seen that each such element was either stressed or unstressed.
  • suitable methods for imprinting residual stress induced magnetically directional characteristics on, i.e., at the surface of, a torque carrying member include, but are not limited to, torsional overstrain; knurling; grinding; mechanical scribing; directed or masked shot peening or sand blasting; roll crushing; appropriate chemical means; selective heat treatments, e.g., induction, torch, thermal print head, laser scribing.
  • knurling allows relatively simple control of the helix angles of the easy axes.
  • knurling permits predetermination of the salient features of the knurl itself, such as pitch, depth and cross-sectional shape and, thereby, allows control of the residual stress induced. It should be appreciated that, in accordance with the present invention, enough of the surface of each band must be stressed that there exists within each band at least one continuous circumferential region which is free of unstressed areas over at least 50% of its circumferential length. Not all knurling is this extensive and care must be taken to select a knurl and a method for applying the knurl which achieves this objective.
  • a knurled band is endowed with shape anisotropy as well as residual stress anisotropy. If it is desired, for example, for compatibility of the knurled shaft with an intended application, the gross shape features of the knurl may be ground off the shaft to leave only magnetic anisotropy caused by residual stress.
  • knurling is not without its substantial shortcomings and, as will be seen hereinafter, is limited in its application to alloys having particular properties.
  • % stressed areas percent of stressed areas along the circumferential length of a circumferential region within each band
  • sensitivity in millivolts/N-M
  • a plot of these parameters yields a curve which has its greatest slope at the lower values of "% stressed areas” and which has a decreasing slope at the higher values of "% stressed areas", up to 100%, at which point the sensitivity is greatest and the slope is close to zero.
  • torque sensor operation at 100% residual stress i.e., at "C” on the curve
  • 100% stressed condition is generally easiest to attain with most methods.
  • acceptable torque sensors can be made which operate at sensitivity levels corresponding to less than 100% residual stress along the length of a circumferential region of the bands.
  • Torque sensors cannot economically and reproducibly be made to operate in the ascending portion AB along the curve in Figure 7 since, in that portion, the sensitivity is extremely responsive to "% stressed areas". This means that even small changes in "% stressed areas” causes relatively large changes in sensitivity. From a practical, commercial standpoint, mass produced torque sensors must have a known and reproducible sensitivity. It would be unrealistic to have to individually calibrate each one. However, even normal production inconsistencies will cause small "% stressed areas” changes which will result, in the AB region of the curve, in large sensitivity differences among sensors. Therefore, commercially useful torque sensors have to operate along a flatter portion of the curve, where the slope is closer to zero. Operating in the BC portion of the curve appears to be an acceptable compromise.
  • the point represented by "B" exceed at least 50%, preferably at least 80%, stressed areas along the circumferential length of a circumferential region. This is in recognition of the fact that the minimum acceptable residual stress loading of a circumferential region is both material and process dependent and that it is generally most desirable to be as close to 100% stress loading as is practical.
  • a 0.25 inch OD cylindrical shaft 100 was formed with two shoulders 102 of equal axial length spaced apart by a reduced diameter shaft portion 104 of 0.215 inch OD.
  • the shaft was formed of a nickel maraging steel commercially available as Unimar 300K from Universal-Cyclops Specialty Steel Division, Cyclops Corporation of Pittsburgh, Pennsylvania and was pre-annealed at 813°C in hydrogen to relieve internal stresses.
  • Each shoulder 102 was carefully knurled using a pair of identical 3/4 inch OD, 3/8 inch long knurling rollers having 48 teeth around their circumference.
  • the shoulders were brought into contact with the knurling rollers in a controlled manner to form symmetrical knurls on each shoulder at angles of ⁇ 30° to the shaft axis. Careful control of the infeed of the tool relative to the shoulders allowed the axial width and depth of each knurl trough to be controlled.
  • the "% stressed areas" along the circumferential length of a circumferential region of each knurled shoulder was determined by assuming that the knurl trough was the only stressed area on the shoulder and that the shoulder surface between troughs was unstressed by the knurling operation; by measuring the trough width and chordal knurl pitch and converting the chordal pitch to circumferential pitch; and by calculating the trough width to circumferential pitch ratio, which ratio when multiplied by 100 represented the desired "% stressed areas” value.
  • the shaft prepared in this manner was affixed to a lever arm which permitted 10-one pound weights to be suspended from cables at each end of the arm. The lever arm was so dimensioned that addition or removal of a single one pound weight from either side represented a torque change on the shaft of 0.5 N-M. By appropriate shifting of the weights, the torque on the shaft could be altered in both magnitude and direction.
  • Figure 9 graphically illustrates the relationship between "% stressed areas” and sensitivity for a shaft prepared as described hereinabove. It can be seen that the curve ascends rapidly up to about 60% stress loading and then appears to level off rather rapidly thereafter. This is because there is believed to be a greater correlation at lower "% stressed area” values between the trough width to circumferential pitch ratio and the actual percentage of stressed areas along the circumferential length of a circumferential region of the shaft. As the width and depth of the knurling trough increases it becomes apparent that the shoulder surface between troughs, at least in the vicinity of the trough edges, becomes slightly deformed and, more than likely, residually stressed.
  • the instant system senses a differential magnetoelastic response to the principal stresses associated with the applied torque between two circumferential bands. The significance of this is that sensing in this manner amounts to sensing the response averaged over the entire circumference of the band. In this manner, sensitivity to surface inhomogenity, position and rotational velocity are avoided.
  • the magnetic discriminator is merely a probe for assessing any differential magnetoelastic response to applied torque between the two bands. In general, it functions by imposing equal cyclically time varying magnetizing forces on both bands and sensing any differences in their resulting magnetization.
  • the magnetizing forces may come from electrical currents, permanent magnets, or both. Resulting magnetization may be sensed through its divergence, either by the resulting flux or its time rate of change.
  • the transducer function is completed by the electrical circuitry which delivers an electrical signal that is an analog of the torque.
  • FIG. 2 One method of supplying the magnetization forces and for measuring the resulting difference signal from the sensing coil is shown in Figures 2 and 3.
  • the bands 6,8 are surrounded by bobbins 16,18 which are concentric with shaft 2.
  • bobbins 16,18 Mounted on bobbins 16,18 are a pair of coils 20,22 and 24,26 of which 22 and 26 are excitation or magnetizing coils connected in series and driven by alternating current and 20 and 24 are oppositely connected sensing coils for sensing the difference between the fluxes of the two bands.
  • a ferrite material core 28 is optionally provided as a generally E-shaped solid of revolution.
  • Circumferential gaps 30 between the shaft and the E-shape core are desirably maintained as small and uniform as is practical to maintain the shaft centered within the core.
  • Figure 3 shows that excitation or drive coils 22,26 are supplied in series from AC source 32 and the emf induced in the oppositely connected sensing coils 20,24 is phase sensitively rectified in the rectifier 34 and is displayed on voltage display instrument 36. Black dots 38 indicate the polarity of the coils.
  • the voltage induced in one of the sensing coils will exceed the voltage induced in the other sensing coil and an output signal representing the difference between the induced voltages and proportional to the applied torque will be obtained.
  • the signal is converted to a direct current voltage in the rectifier 34 and the polarity of the rectifier output will depend upon the direction, i.e., CW or CCW, of the applied torque.
  • the a.c. driving current should advantageously be maintained in the range 10 to 400 milliamperes at excitation frequencies of 1 to 100 kHz.
  • Figure 4 illustrates another type of magnetic discriminator for sensing the permeability change of the bands upon application of a torque to the shaft.
  • Magnetic heads 42,44 comprising a ferromagnetic core and a coil wound thereupon are provided in axial locations along shaft 40 which coincide with bands 46,48 and are magnetically coupled to the bands.
  • the magnetic heads 42,44 are excited by high frequency power source 50 through diodes 52,54. With no torque applied to shaft 40, the magnetic permeability of the bands are equal. Therefore, the inductance levels of both magnetic heads are equal and opposite in polarity, and the net direct current output, V out , is zero.
  • V out direct current output
  • the inductance of one magnetic head increases while the inductance of the other decreases, with a resultant difference in excitation current between the heads.
  • This difference in excitation current passed via output resistors 56 and smoothing capacitor 58, produces a direct current output signal which has polarity and magnitude indicative of the magnitude and direction of the applied torque.
  • a shaft of suitable material is endowed in each of two proximate bands with symmetrical, left and right handed helical magnetic easy axes. At least in the region of the bands, and more commonly over its entire length the shaft is formed, at least at its surface, of a material which is ferromagnetic and magnetostrictive.
  • the material must be ferromagnetic to assure the existence of magnetic domains and must be magnetostrictive in order that the orientation of the magnetization may be altered by the stresses associated with an applied torque. Many materials are both ferromagnetic and magnetostrictive.
  • desirable materials which also exhibit other desirable magnetic properties such as high permeability, low coercive force and low inherent magnetic anisotropy.
  • desirable materials have high resistivity in order to minimize the presence of induced eddy currents as a result of the application of high frequency magnetic fields.
  • favored materials must retain these favorable magnetic properties following the cold working and heat treating necessary to form them into suitable shafts having appropriately high strength and hardness for their intended use.
  • the nickel maraging steels possess the unusual combination of superior mechanical properties and outstanding and thermally stable magnetic properties which give them a special suitability and make them particularly advantageous for use in all magnetoelastic torque transducers in which a magnetic field is applied to ferromagnetic, magnetostrictive means and the change in permeability caused by torque applied thereto is sensed to obtain an indication of the magnitude of the applied torque.
  • the nickel maraging steels are, typically, extra-low-carbon, high nickel, iron-base alloys demonstrating an extraordinary combination of structural strength and fracture toughness in a material which is readily weldable and easy to heat-treat. They belong to a loosely knit family of iron-base alloys that attain their extraordinary strength characteristics upon annealing and during cooling, by transforming to an iron-nickel martensitic microstructure, and upon aging in the annealed or martensitic condition. Thus, the alloys are termed "maraging" because of the two major reactions involved in their strengthening --martensitizing and aging. However, these steels are unique due to their high nickel and extremely low carbon content, which permits formation of an outstandingly tough martensite that can be strengthened rapidly to extraordinarily high levels. Yield strengths up to and well beyond 300 ksi are available in these steels in the aged condition.
  • Typical nickel maraging steels are alloys comprising 12-25% Ni, 7-13% Co, 2.75-5.2% Mo, .15-2.0% Ti, .05-0.3% Al, up to 0.03% C, balance Fe and incidential amounts of other elements, such as Mn, Si, S, P, Cb.
  • the most popular and practically significant maraging steels, at least at present, are the 18% Ni steels which can be aged to develop yield strengths of about 200 ksi, 250 ksi and 300 ksi.
  • 18Ni200, 18Ni250 and 18Ni300 grade maraging steels have typical compositions in the ranges 1-19% Ni, 7-9.5% Co, 3.0-5.2% Mo, 0.1-0.8% Ti, .05-.15% Al, up to 0.03% C, balance Fe and incidential amounts of other elements.
  • the 18% nickel maraging steels are heat treated by annealing at temperatures of 1500°F and above for a sufficient time, e.g., one hour per inch of thickness, to dissolve precipitates, relieve internal stresses and assure complete transformation to austenite.
  • the 18% Ni steels are conventionally aged at 750-1100°F, desirably 900-950°F, for 3 to 10 hours, depending upon thickness, usually 3-6 hours.
  • 750-1100°F desirably 900-950°F
  • 3 to 10 hours depending upon thickness, usually 3-6 hours.
  • satisfactory strength characteristics and superior magnetic characteristics can be attained in alloys aged for as little as 10 minutes.
  • Ni maraging steels are cobalt-free 18% Ni maraging steels as well as cobalt-containing 25% Ni, 20% Ni and 12% Ni maraging steels.
  • the 18% Ni-cobalt containing maraging steels are commercially available from a number of sources.
  • VascoMax C-200, VascoMax C-250, VascoMax C-300 and VascoMax C-350 are obtainable under the trademarks VascoMax C-200, VascoMax C-250, VascoMax C-300 and VascoMax C-350 from Teledyne Vasco of Latrobe, Pennsylvania; under the trademarks Marvac 250 and Marvac 300 from Latrobe Steel Company of Latrobe, Pennsylvania; under the trademark Unimar 300K from Universal-Cyclops Specialty Steel Division, Cyclops Corporation of Pittsburgh, Pennsylvania; and, under the trademark Almar 18-300 from Superior Tube of Norristown, Pennsylvania.
  • the 18% Ni-cobalt free maraging steels are commercially available under the trademarks VascoMax T-200, VascoMax T-250 and VascoMax T-300 from Teledyne Vasco of Latrobe, Pennsylvania.
  • Ni maraging steel refers to alloys of iron and nickel which contain from 9-25% nickel and which derive their strength characteristics from iron-nickel martensite formation, as hereinbefore described.
  • the nickel maraging steels have excellent magnetic properties which make them outstanding for use as the magnetic material in non-contact torque transducers.
  • they have high and substantially isotropic magnetostriction, in the range of 25 ppm ⁇ 15 ppm, and do not exhibit a Villari reversal; high electrical resistivity; low inherent magnetic anisotropies due to crystalline structure; high magnetic permeability; low coercive force, in the range 5-25 oersted; and, stability of magnetic properties with alloy chemistry.
  • most important is that their magnetic properties are only modestly, yet favorably, affected by strengthening treatments -- indeed, their magnetic properties improve with cold work and aging heat treatment.
  • the coercive force of an 18% Ni maraging steel in fact decreases when aged at 900°F for up to 10 hours.
  • the maraging steels can be advantageously used in their aged condition, i.e., in a condition where they exhibit maximum strength characteristics and substantially the same or improved magnetic characteristics.
  • maraging steels as the magnetic material in a magnetoelastic torque sensor, particularly as the shaft material in a device whose torque is to be sensed, obviates virtually all of the objections heretofore made to using the device shaft as the magnetic member.
  • the mechanical and strength properties of maraging steels satisfy the mechanical properties requirements for most all shaft applications while, at the same time, providing outstanding magnetic properties for its role in the torque sensor. Aging of the maraging steels provides the high strength and high hardness needed for the mechanical application without loss of magnetic permeability or increase in coercive force.
  • the conventional manner of heat treating maraging steel including the initial solution anneal at temperatures in excess of 1500°F, relieves internal stresses due to mechanical working and most stresses due to inhomogeneities and crystal orientation, thus minimizing the amount of random magnetic anisotropy in a maraging steel shaft.
  • heat treatment is combined with the creation, according to the present invention, of a pair of adjacent bands endowed with intentionally instilled magnetic stress anisotropy of a relatively large magnitude, e.g., by stressing the shaft beyond its elastic limits with applied stresses of a magnitude greater than the largest torque stresses anticipated during normal usage of the shaft, the contribution to total magnetic anisotropy of any random anisotropy in the shaft is indeed negligible.
  • the advantage of the nickel maraging steels in magnetoelastic torque transducers can be realized by forming the shaft of the desired nickel maraging steel, by forming a region of the shaft of the desired nickel maraging steel and locating the annular bands within this region, or by surfacing with a nickel maraging steel a shaft formed of an alloy having mechanical properties suitable for the intended function of the shaft, i.e., applying over at least one complete circumferential region of suitable axial extent of the shaft a surfacing alloy of the desired nickel maraging steel and locating the annular bands within this region.
  • the surfacing process need apply a circumferential layer of thickness not exceeding about 0.015 inches.
  • the surfacing process selected may advantageously be selected from among the many known additive processes, e.g., electroplating, metal spraying, sputtering, vacuum deposition, ion implanatation, and the like.
  • a torque transducer was assembled using a 12.7 mm diameter cylindrical shaft having formed thereon a pair of axially spaced-apart bands endowed with helically symmetrical LH and RH magnetic easy axes.
  • the bands each had an axial length of 12.7 mm and were separated by a 12.7 mm shaft segment. They were formed by knurling using a 3/4-inch OD knurling tool having 48 teeth around the circumference, each tooth oriented at 30° to the shaft axis.
  • each bobbin having a magnetizing and sensing coil mounted thereon.
  • the magnetizing coils were connected in series and driven by an alternating current source having a 10 KHz frequency output and a 200 mA peak driving current.
  • the emf induced in each of the sensing coils was separately rectified with the rectified outputs oppositely connected to produce a difference signal which was displayed on a voltage display instrument.
  • Four shafts were employed, identical in all respects except they were each formed of different materials. The composition of each shaft is set forth in percent by weight hereinbelow:
  • the T-250 nickel maraging steel shaft was used in the solution annealed, unaged condition as received from Teledyne Vasco. Likewise, the other shafts were also used in their as-purchased condition without further heat treatment. A known torque loading was applied to each shaft under test and the output voltage signal was recorded. The applied torque was increased from zero up to 100 newton-meters (N-M).
  • Figure 5 is a graph of applied torque versus output d.c. voltage for each shaft. It is apparent that the sensitivity of the T-250 shaft in terms of magnitude of output signal for a given torque loading was significantly greater than for the other shaft materials tested. In addition, the linearity of the output signal for the T-250 shaft was extremely good over the entire torque range. The other shaft materials appeared to be about equally insensitive, compared to the T-250 shaft, to applied torque. None produced as linear a signal as the T-250 shaft, although each produced a reasonably linear signal over most of the torque range.
  • the T-250 nickel maraging steel shaft was aged at about 900°F for 30 minutes to improve the strength and hardness of the shaft.
  • the other shafts were heat treated in the same manner, after which each shaft was subjected to an applied torque from zero to 100 N-M and the output d.c. voltage recorded.
  • Figure 6 is a graph of applied torque versus output d.c. voltage for each shaft after heat treatment. It can be seen that once again the sensitivity of the T-250 shaft far exceeded the sensitivity of the other shafts and once again the T-250 output signal was linear over the entire torque range.
  • the better procedure for preparing a magnetoelastic torque transducer in accordance with the present invention from a non-Ni maraging steel alloy such as SAE 9310 is to first thermally harden the alloy, as by case hardening, and then machine the resulting shaft as needed to straighten it. Thereafter, grinding or other processing of the hardened alloy can be accomplished to provide bands endowed with residual stress created magnetic anisotropy.
  • One advantage of the use of grinding is that it removes any surface anisotropies instilled by the straightening process and substitutes the desired residual stress-created anisotropies, all without macroscopic topographic alteration of the shaft surface.
  • Figures 5 and 6 graphically illustrate the signal response to applied torque using a relatively low, 10 kHz, a.c. excitation frequency. It has been found that the output signal is directly proportional to and increases approximately linearly with a.c. frequency. Tests show that at 20 kHz, for example, a doubling of the output d.c. voltage signal is obtained.
  • a.c. frequencies in the range 1-100 kHz can advantageously be used to drive torque transducers of the present invention. Preferably, frequencies of 10-30 kHz, just above the human audible range, are used in order to avoid whistling. Most desirably, the frequency is adjusted to about 20 kHz.
  • the signal also appears to be directly proportional to, more specifically to vary sigmoidally with, the drive current which, depending upon the frequency, can usefully be in the range 10-400 mA (peak). Generally, sufficient current is used to obtain a good signal at the chosen frequency and, desirably, to adjust the signal hysteresis to zero over the entire applied torque range.
  • the Sasada et al sensitivity corrected to an equivalent basis as that shown in Figure 6 hereof is 0.007 V/N-M.
  • the torque transducer of the present invention is more than twice as sensitive as the amorphous ribbon torque sensor of Sasada et al.
  • thermally hardenable steel alloys can be made to function very effectively in the magnetoelastic torque transducers of the present invention.
  • This can be accomplished with such alloys by creating the residual stress within the bands only after the alloys have been appropriately thermally treated to bring their hardness and strength characteristics up to the levels required by the intended usage of the alloys.
  • the subsequent or post-hardening creation of residual stress to endow the bands with the desired magnetic anisotropy does not adversely alter the mechanical or strength properties of the alloys.
  • preparing a steel alloy shaft in this manner does impose strict limitations on the type of process which may be used to create the residual stresses.
  • the use of thermally hardenable non-Ni maraging steel alloys, as defined hereinafter, in the magnetoelastic torque transducers of the present invention is limited to creating the necessary residual stresses only after the alloy has been mechanically strengthened by thermal treatment and, then, only by selected residual stress creating processes which are capable of endowing the bands with the desired corresponding and opposite uniform distribution of magnetic anisotropy.
  • Such processes include, but are not limited to, grinding, mechanical scribing (with appropriate tools), directed or masked shot peening or sand blasting, chemical means and heat treatments, including laser scribing, induction, torch, thermal print head, and the like.
  • the non-Ni maraging steel alloys play an important role as the ferromagnetic, magnetostrictive shaft element in the magnetoelastic torque transducers of the present invention.
  • differential macroscopic topographic alteration of the shaft surface such as knurls, slits, ridges, etc.
  • the non-magnetoelastic effect on permeability sensing of differential topographic alteration is threefold.
  • There is a material induced, non-uniform, topographic effect as a result of which the shape and material symmetry in each band is differently altered or distorted when the shaft is subjected to torque. Due to the resolution of an applied torsional stress into orthogonal tensile and compressive stresses, the knurls, slits, etc.
  • This topographic effect causes the torsional stresses in the bands to distribute differently than they otherwise would in a topographically unaltered band with the result that at least a part of the permeability changes sensed by coils overlying the bands will be due to this topographically influenced stress distribution and not solely due to the desired magnetoelastic effect. Finally, there is the effect on permeability sensing caused by the shape of the topographic alteration.
  • the bands consisted, respectively, of ⁇ 45° slits formed in the shaft surface
  • a torsional stress is applied to the shaft and a cyclically time varying magnetic field is applied to the bands, depending upon whether the torsional stress is applied CW or CCW
  • one of the tensile/compressive stresses tends to align the magnetization along the length of one set of slits while the other tends to align the magnetization orthogonally thereto, i.e., in a direction perpendicular to the length of the other set of slits.
  • magnetoelastic considerations it is, as a physical and configurational matter, easier for the applied magnetization to move along the former than the latter.
  • the permeability sensed by the coil overlying the band in which the magnetization seeks to align along the length of the slits is higher than the permeability sensed by the coil overlying the band in which the magnetization seeks to align across the length of the slits.
  • This increase in permeability is due in part to the topographic alteration of the band surface. The magnetization is forced to follow a physically more difficult path in moving across rather than along the slits.
  • a section taken perpendicualr to the shaft axis in either band is a circle with only microscopic deviations from a perfect circle.
  • the grinding technique has created two adjacent bands having opposite and corresponding magnetic anisotropy due substantially completely to residual stress created by the grinding process.
  • torsional stress is applied to the shaft there is no material-induced, non-uniform topographic effect, such as lengthening or shortening of ridges or troughs; there is no topographically-induced differential torsional stress distribution because the topographics of the bands are identical; there is no shape effect due to any topographic differential between the bands. This differs significantly from the situation which exists when knurled regions form the bands.
  • Each knurled region contains different arrangements of troughs and ridges, i.e., distortable shapes and features, differential stress and magnetization influencing topographics, and shape effect imparting features, which separately and cumulatively alter the sensed permeability independent of the residual stress created anisotropy intentionally instilled in the bands.
  • troughs and ridges i.e., distortable shapes and features, differential stress and magnetization influencing topographics, and shape effect imparting features, which separately and cumulatively alter the sensed permeability independent of the residual stress created anisotropy intentionally instilled in the bands.
  • the magnetizing coils were connected in series and driven by an alternating current source.
  • the emf induced in each of the sensing coils was separately rectified with the rectified outputs oppositely connected to produce a difference signal which was displayed on a voltage display instrument.
  • the characteristics of the arrangement were sensed on the 1/4-inch diameter shafts using a conventional multivibrator circuit in which only one of two parallel transistors at a time conducts the input from a high frequency source, thus allowing a square wave voltage to create a cyclically time varying magnetic field for application to the bands on the shaft with the result that the inductance of a coil associated with one of the bands increases while the inductance of a coil associated with the other of the bands decrease. This difference in inductance produces different voltage signals which enter a comparator for producing a difference signal which was displayed on a voltage display instrument.
  • the materials were T-250, a nickel maraging steel hardened by martensitizing and aging; AISI 416, a through hardened steel; and, SAE 9310, a case hardened steel.
  • the compositions of each alloy are set forth in percent by weight hereinbefore.
  • each of the alloys was ground in its unhardened condition to form the desired bands of residual stress-created magnetic anisotropy.
  • a known torque loading was applied to each shaft under test and the output voltage signal was recorded. The applied torque was increased from zero up to as high as 30 newton-meters (N-M) with some shafts.
  • Figure 10, curve “1” (SAE 9310), Figure 11, curve “3” (AISI 416) and Figure 12, curve "5" (T-250) are graphs of applied torque versus output d.c. voltage for each shaft ground in the unhardened condition and tested.
  • the total quiescent anisotropy ("K") of the alloy shaft system (including anisotropy resulting from residual stresses, shape, crystallinity, etc.) before the application of torsional stress to the shaft is higher for a hardened than for a soft alloy shaft.
  • K quiescent anisotropy
  • the permeability effect of an applied stress is directly proportional to the magnetostriction of the alloy and the applied stress and is inversely proportional to the quiescent anisotropy of the system. Therefore, when torque is applied to a high "K” system, the effect of the applied stress is smaller and the observed sensitivity or effect on permeability is likewise smaller.
  • the higher "K” causes a lower hysteresis and improved linearity.
  • effective magnetoelastic torque transducers in accordance with the present invention can be made using nickel maraging steel as the ferromagnetic and magnetostrictive shaft component and instilling desired magnetic anisotropy in the shaft by creating residual stress within the bands either before or after the nickel maraging steel alloy has been aged to improve its mechanical and strength properties. It has also been noted that effective magnetoelastic torque transducers in accordance with the present invention can be made using selected non-Ni maraging steel alloys and creating the residual stress within the bands only after the non-Ni maraging steel alloys have been appropriately thermally treated to improve their mechanical and strength characteristics. It is clear for many reasons that not all non-Ni maraging steel alloys can be so employed.
  • the magnetostriction i.e., the functional change in length in an applied magnetic field
  • the alloy undergoes a Villari reversal -- it first expands with increasing field strength, i.e., the fractional change in length is positive, and then contracts, i.e., the fractional change in length is negative with increasing field strength.
  • the stress-applied anisotropy affects the existing random anisotropy differently in shaft areas of positive magnetostriction than in areas of negative magnetostriction.
  • non-Ni maraging steel alloys useful as the ferromagnetic, magnetostrictive region of or associated with the rotating shaft should have a substantially isotropic, high magnetostriction having an absolute value of at least 5 ppm; been hardened by thermal treatment; a carbon content, in percent by weight, in the range from 0.05 to 0.75 percent; an alloy composition tailored to the mechanical, chemical and magnetic (resulting anisotropy and magnetostriction) requirements of the intended application of the shaft.
  • non-Ni maraging steel alloy useful in the present invention from thermally hardened steel alloys characterized by an isotropic magnetostriction having an absolute value of at least 5 ppm and a composition comprising the following elements in the indicated proportions: FeC a M b Q c wherein "M” is one or more alloying elements selected from the group consisting of Ni, Cr, Co, Ti, Al, Mn, Mo, Cu and B, "Q” is one or more other alloying elements including, but not limited to, common steel alloying elements such as silicon (Si), phosphorous (P), sulfur (S), nitrogen (N), selenium (Se), tungsten (W), vanadium (V), hafnium (Hf), columbium (Cb), tantalum (Ta) and tin (Sn); "a” indicates a carbon content of from .05 to 0.75 percent by weight; “b” indicates a content of alloying element(s) "M” at least sufficient to raise the
  • the magnetostriction of the alloys can be at least estimated.
  • the presence of 12.3% Cr is primarily responsible for raising the magnetostriction of the alloy to about 20 ppm
  • the presence of 5% Cr and 0.8 Mn are primarily responsible for raising the magnetostriction of the alloy to about 7 ppm
  • SAE 9310 the presence of 3-3.5% Ni and 1-1.4% Cr are primarily responsible for raising the magnetostriction of the alloy to about 15 ppm.
  • the unique and improved magnetoelastic torque transducers of the present invention are broadly useful for the sensing and measurement of torque in members of all types and sizes, whatever may be the device or field of application in which the member operates. It is universally accepted that torque is an absolutely fundamental parameter in the control of systems having rotating members. Sensing the instantaneous torque experienced by a rotating member and generating an electrical current in response thereto which bears a known relationship to the torque allows the early diagnosis of incipient problems or the control, via microprocessor or otherwise, of the engine, machine, motor, etc. which drives the rotary member.
  • torque transducers of the present invention can be found in virtually every device having a rotating member.
  • torque transducers such as are provided in accordance with the present invention for controlling heavy industrial machinery of all types, e.g., pulp grinders for maintaining fiber quality, paper-making machines, and the like, as well as for use in consumer home and commercial appliances, e.g., food mixers and processors.
  • heavy industrial machinery e.g., pulp grinders for maintaining fiber quality, paper-making machines, and the like
  • consumer home and commercial appliances e.g., food mixers and processors.
  • small, inexpensive, sensitive, reliable torque sensors has been noted in such diverse applications as machine tools, hand tools, robotics, information devices, industrial measuring instruments, weighing systems of various kinds, electronic power assisted power steering, and vehicular traction balancing.
  • the torque sensor of the present invention is capable of recovering the torque signature of an engine over a wide enough bandwidth to discern salient details of important torque contributing events at all points between idle and the top operating speed of the engine. Torque sensing in an accurate and cost effective manner enables early diagnosis of incipient problems due to the functional condition of the engine, helps to avoid unanticipated failures that might limit the servicability of the vehicle at critical times and improves and/or controls the performance and economy of the engine and its power drive.
  • the torque sensing system In a 12 cylinder, 4 stroke engine operating at 4000 rpm there are 400 power strokes and (at least) 1600 valving events (openings or closings) every second. Turbine engines run with far smoother power input but at speeds up to 500 revolutions per second. To be capable of discriminating important details of these salient events, the torque sensing system must have a reasonably flat frequency response up to at least several times the maximum event rate, i.e., in the vicinity of 5 kHz. The frequency response must also extend downward to zero Hz to faithfully capture the steady state torque components imposed by the vehicle loads.
  • a torque sensor having 5 kHz bandwidth capability cannot be positioned arbitrarily. While torque is applied to the engine shaft by contact forces at discrete locations, it is transmitted axially by continuous stress distributions. Transient torque events are not transmitted instantaneously nor do they remain unaltered along the shaft. The finite elasticity and inertia of real shaft materials combine to limit the transmittable rate of change of torque. Steep transients trigger oscillatory exchanges of elastic and kinetic energy (stress waves) which travel with material and mode dependent characteristic velocities along the shaft. The fidelity of the transmitted torque is further reduced with distance from its source by the accumulated dissipative effects of internal and external friction. The sensor must therefore be located close enough to the source(s) to avoid losing the desired torque information either by attenuation or in background "noise" composed of complex combinations of interfering and reflecting stress waves.
  • Important sensor requirements are that it be small, at least in the dimension parallel to the shaft axis, that it be rugged and that it be free from deteriorating effects of use or time such as wear, corrosion or fatigue.
  • the sensor should be amenable to performance verification and calibration, especially in the event of repair or replacement of parts of the torque sensing system, including the engine shaft. It should have neglible impact on engine and drive line manufacturability, operation and maintenance and, under no circumstances should the failure of the torque sensor have any contingent consequences which interfere with the otherwise normal operation of the vehicle.
  • a suitable torque sensor should be an unobtrusive device that is difficult to abuse and is capable of reliably recovering much of the torque information available on the torqued shaft. None of the heretofore contemplated state of the art torque transducers can meet these requirements. However, the magnetoelastic torque sensors of the present invention appear eminently suitable in all respects and will, for the first time, make inexpensive, reliable and sensitive torque sensors available for commerical implementation.

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EP90125788A 1986-12-05 1987-12-03 Magneto-elastischer Drehmomentwandler Expired - Lifetime EP0422702B1 (de)

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US06/938,404 US4760745A (en) 1986-12-05 1986-12-05 Magnetoelastic torque transducer
US938404 1986-12-05
US07/119,531 US4896544A (en) 1986-12-05 1987-11-17 Magnetoelastic torque transducer
US119531 1987-11-17
EP87117920A EP0270122B1 (de) 1986-12-05 1987-12-03 Magneto-elastischer Drehmomentwandler

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Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5343759A (en) * 1991-07-08 1994-09-06 Skf Nova Ab Sensor system
EP0523025A1 (de) * 1991-07-08 1993-01-13 Scan-Mag Sense AS Verfahren zum Messen eines Drehmomentes und/oder axialer Spannungen
US5412582A (en) * 1991-07-08 1995-05-02 Hesthamar; Tore Surveillance system
US5591925A (en) * 1991-07-29 1997-01-07 Garshelis; Ivan J. Circularly magnetized non-contact power sensor and method for measuring torque and power using same
US5706572A (en) * 1991-07-29 1998-01-13 Magnetoelastic Devices, Inc. Method for producing a circularly magnetized non-contact torque sensor
EP0525551A3 (en) * 1991-07-29 1993-06-09 Ivan J. Garshelis Circularly magnetized non-contact torque sensor and method for measuring torque using same
US5465627A (en) * 1991-07-29 1995-11-14 Magnetoelastic Devices, Inc. Circularly magnetized non-contact torque sensor and method for measuring torque using same
US5520059A (en) * 1991-07-29 1996-05-28 Magnetoelastic Devices, Inc. Circularly magnetized non-contact torque sensor and method for measuring torque using same
EP0525551A2 (de) * 1991-07-29 1993-02-03 Magnetoelastic Devices Inc. Berührungsfreie kreisförmig magnetisierter Drehmomentsensor und Drehmomentmessverfahren damit
US5708216A (en) * 1991-07-29 1998-01-13 Magnetoelastic Devices, Inc. Circularly magnetized non-contact torque sensor and method for measuring torque using same
US5351555A (en) * 1991-07-29 1994-10-04 Magnetoelastic Devices, Inc. Circularly magnetized non-contact torque sensor and method for measuring torque using same
US5887335A (en) * 1991-07-29 1999-03-30 Magna-Lastic Devices, Inc. Method of producing a circularly magnetized non-contact torque sensor
US6490934B2 (en) 1991-07-29 2002-12-10 Magnetoelastic Devices, Inc. Circularly magnetized non-contact torque sensor and method for measuring torque using the same
US6145387A (en) * 1997-10-21 2000-11-14 Magna-Lastic Devices, Inc Collarless circularly magnetized torque transducer and method for measuring torque using same
US6260423B1 (en) 1997-10-21 2001-07-17 Ivan J. Garshelis Collarless circularly magnetized torque transducer and method for measuring torque using same
US6047605A (en) * 1997-10-21 2000-04-11 Magna-Lastic Devices, Inc. Collarless circularly magnetized torque transducer having two phase shaft and method for measuring torque using same
US6553847B2 (en) 1997-10-21 2003-04-29 Magna-Lastic Devices, Inc. Collarless circularly magnetized torque transducer and method for measuring torque using the same
DE102011080343A1 (de) * 2011-08-03 2013-02-07 Siemens Aktiengesellschaft Verfahren zur Erkennung von Gegenständen und Verwendung eines magnetoelastischen Sensors

Also Published As

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DE3772940D1 (de) 1991-10-17
JPH0831636B2 (ja) 1996-03-27
AU8196587A (en) 1988-06-16
NZ235662A (en) 1993-04-28
DE3750041D1 (de) 1994-07-14
CA1304601C (en) 1992-07-07
EP0270122A2 (de) 1988-06-08
US5052232A (en) 1991-10-01
EP0270122B1 (de) 1991-09-11
US4896544A (en) 1990-01-30
ATE67307T1 (de) 1991-09-15
AU600537B2 (en) 1990-08-16
DE3750041T2 (de) 1994-11-17
JPH08293634A (ja) 1996-11-05
NZ222745A (en) 1993-04-28
ATE107023T1 (de) 1994-06-15
JPS63252487A (ja) 1988-10-19
CN1014829B (zh) 1991-11-20
EP0422702A3 (en) 1991-07-24
KR880008012A (ko) 1988-08-30
EP0270122A3 (en) 1989-03-22
EP0422702B1 (de) 1994-06-08
KR920006454B1 (ko) 1992-08-06
IN170371B (de) 1992-03-21
CN87108230A (zh) 1988-07-27

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